Hurricane Irene's fury is growing and the National Hurricane Center warned today that the storm could be upgraded from its current level of Category 3 to a more ominous Category 4 by Thursday.

The core of the hurricane is expected to move across the southeastern and central Bahamas tonight, with maximum winds near 120 mph.

As the storm clears the island and continues over the warm water of the Atlantic, its wind speed is expected to strengthen and the size of the storm could increase, the Hurricane Center predicted.

"Warm water is essentially like their fuel. It helps them strengthen and it's got plenty of that ahead of it, at least in the next few days," said John Cangialosi, a hurricane specialist at the National Hurricane Center.

Forecasters predict Irene could hit the Outer Banks of North Carolina on Saturday, move up to the mid-Atlantic region including Maryland, Delaware and New Jersey late Saturday or early Sunday, and hit New England late Sunday.

The storm is shaping up to be the most powerful hurricane to strike the East Coast of the United States in years and thousands of people in Ocracoke Island, N.C., have been ordered to evacuate as the storm bore down on the frgile islands of North Carolina's Outer Banks. The island is reachable only by ferry.

Cangialosi also said that hurricanes fluctuate in strength and size, so two days of strengthening could be followed by weakening as the storm moves north.

"It loses strength considerably when it tracks over cooler water," he said. "For the next couple of days, the general theme is that it will probably continue to strengthen."

Officials tonight told visitors in North Carolina's Dare County which includes Nags Head and heavily populated northern Outer Banks to evacuate by 8 a.m. Thursday.

An updated bulletin from the National Hurricane Center said that the "extremely dangerous" storm will raise water levels by as much as seven to eleven feet above normal tide levels in the Bahamas, potentially causing "life-threatening flash floods and mud slides in areas of steep terrain" as well as "life-threatening surf and rip current conditions."

Hurricane Irene went from a Category 2 to Category 3 from Tuesday night to this morning after ripping street signs out of the ground in the Turks and Caicos and destroying buildings in the Dominican Republic.

Craig Fugate, the manager of the Federal Emergency Management Agency, urged those from the Mid-Atlantic region to New England to start preparing now for the possibility of the hurricane's landfall.

"It's going to be close and whether we get a brush or whether we have a landfall, it's too early to say," Fugate said. "Go ahead and make sure you're ready and then if evacuations are required, heed those evacuation orders. The Hurricane Center says this storm is going to grow and strengthen...and it's really something people need to be prepared now for so they can be ready if they have to act."

Fugate referenced Tuesday's surprise 5.8 magnitude earthquake to urge those living in the Northeast to prepare.

"It's again a reminder that we don't always get to pick the next disaster," Fugate said. "We know this hurricane is coming this way. We just don't know where it's going to hit or how bad it will get. So take time now to get ready."

The hurricane's winds stretch over 400 miles. That's the same width as the entire state of Arizona. The Caribbean islands are low and flat which only fuels the strength of the hurricane, meteorologists say. The storm's surge is 7 to 11 feet, meaning that waters are 7 to 11 feet higher in the Caribbean.

Business owners hurried to board up their stores in the Bahamas and tourists started lining up at airports to get out of harm's way.

Hurricane Irene Pounds Caribbean

Honeymooners Jennifer and Todd Napier spent Tuesday at the airport booking flights and looking for hotels on their laptop.

"We tried to book a flight yesterday. They wanted to charge us $2,500 extra so we were like, no, we'll just wait it out and then our hotel made an emergency announcement and told us they're going to kick us out," Todd Napier said.

Shannon Drury didn't just leave her hotel, she was told the whole Bahamian island of Eleuthera would have to evacuate with officials telling her the danger was "catastrophic."

Fran Newman plans to ride out the storm in the Bahamas.

"The hotel has already told us the plans they have for us should there be a major storm and I am comfortable with the plans they have," she said.